The present invention relates to surface modified silica, methods of making and using the same.
The use of silica as a reinforcing filler has been gaining wide acceptance in a variety of fields. There has also been many attempts in the prior art to treat the surface of precipitated silica to improve the properties of the precipitated silica for use as a reinforcing filler.
Griffith et al., U.S. Pat. No. 5,908,660, disclose a method for preparing hydrophobic silica precipitated silica. The method disclosed by the Griffith et al. reference comprises two steps. The first step involves contacting an aqueous suspension of precipitated silica with an organosilicon compound in the presence of a catalytic amount of an acid to effect hydrophobing of the precipitated silica. In the second step the aqueous suspension of the hydrophobic precipitated silica is contacted with a water-immiscible organic solvent to effect the separation of the hydrophobic precipitated silica from the aqueous phase.
It is important to note that the term xe2x80x9cparticlexe2x80x9d, as used in this disclosure, differs from the use of the term as used by others, such as Griffith ""660, in that particles described herein are those referred to by those familiar with the art as xe2x80x9cprimary particlesxe2x80x9d. These are individual, generally spherical units, formed at the early stages of the silica synthesis process, which cannot be subdivided by ordinary means. The measurement of the diameters of these particles (as by electron microscopy), together with the determination of their surface area (as by nitrogen adsorption), will reveal a particle density essentially identical to that of pure silica (about 2.21 g/cm3). Further, the term xe2x80x9caggregatexe2x80x9d, as used herein, refers to an accumulation of these particles that are tightly held together. Aggregates generally cannot be broken down into particles through mechanical means, particularly when aggregates are being mixed with other materials in a mixing operation. The particle-particle interaction forces are generally too great to be broken.
The term xe2x80x9cagglomeratexe2x80x9d refers to an accumulation of aggregates that are held together. Agglomerates are generally held together by weaker physical forces and can be separated by mechanical means, such as during a mixing operation. Unfortunately, the Griffith et al reference mischaracterizes precipitated silica as aggregate silica. However, it is widely known and accepted to one having ordinary skill in the art that precipitated silica can only exist in the agglomerated form, not in the aggregate form.
Parmentier et al., U.S. Pat. No. 5,009,874, disclose a method for making a hydrophobic, essentially spheroidal precipitated silica, useful as a reinforcing filler in silicone elastomers. In a first step the precipitated silica in aqueous suspension is hydrophobed with an organosilicon compound. In a second step a water immiscible organic solvent is added to effect separation of the hydrophobic precipitated silica from the aqueous phase. The water immiscible organic solvent is added to the process at a volume (L) to weight (kg) ratio of silica of from 1 to 5 and preferably from 1.5 to 4.5.
Nauroth et al., U.S. Pat. No. 4,208,316, U.S. Pat. No. 4,273,589 and U.S. Pat. No. 4,308,074, disclose the treatment of dried precipitated silica with organosilicon compound hydrophobing agents in a ratio of 10:0.5 to 10:3. The product obtained thereby is tempered for 60 to 180 minutes, preferably 70 to 130 minutes, at a temperature of 200xc2x0 C. to 400xc2x0 C.
Reinhardt et al., U.S. Pat. No. 4,072,796, disclose a process where an acidic wet suspension of precipitated silica at a temperature of about 50xc2x0 C. to 90xc2x0 C. is hydrophobed with a prepolycondensed organohalosilane or a prepolycondensed mixture of organohalosilanes. The hydrophobed precipitated silica is filtered, washed, dried, and tempered at about 300xc2x0 C. to 400xc2x0 C.
Reinhardt et al., U.S. Pat. No. 4,015,031, disclose a process where a precipitated silica in powdered form is heated to a temperature of about 200xc2x0 C. to 300xc2x0 C. with agitation to fluidize and then treated dropwise with an organosilane which is stable and boils below 300xc2x0 C.
Treblinger et al., U.S. Pat. No. 3,904,787, disclose the treatment of a precipitated silica in aqueous suspension with an organohalosilane at a temperature within a range of 15xc2x0 C. to 70xc2x0 C. The hydrophobic precipitated silica is filtered, washed, dried, and tempered by heating in the range of 200xc2x0 C. to 500xc2x0 C.
Although all of the prior art attempts described hereinabove are methods to treat agglomerated precipitated silica, none of the references attempt to stabilize the surface of non-agglomerated silica.
There have been alternative attempts to provide stabilized non-agglomerated silica. Once such attempt is described in European Patent Publication No. 881192, which is a process for producing a hydrophobic organosilica sol comprising a colloidal silica stabilized and dispersed in a hydrophobic organic solvent, which does not contain agglomerate. The stabilized silica of this reference is prepared in a solvent, such as ketones and esters, which are not compatible with rubber synthesis techniques. Therefore, it remains desirable in the art to provide surface-stabilized, non-agglomerated silica that is compatible with rubber compositions and rubber synthesis.
It would be advantageous to employ stabilized non-agglomerated silica for purposes of reinforcing rubber compositions to avoid the need to divide the large agglomerates of precipitated silica into smaller aggregates. The use of non-agglomerated silica, results in the reduction of energy costs in rubber compounding, and also avoids degradation of the polymer that is traditionally associated with the division of large agglomerates of precipitated silica into smaller silica particles.
The present invention provides a process for preparing surface-stabilized, non-agglomerated silica dispersed within a polymer. The process of the present invention comprises the steps of providing colloidal silica; stabilizing the surface of the colloidal silica; and blending the surface-stabilized silica with a polymer solution and, optionally, at least one additive, thereby substantially preventing agglomeration of silica.
The present invention further provides a surface-stabilized, non-agglomerated silica dispersed in a polymer, wherein the silica size is less than about 50 nanometers.
The present invention also provides a process for preparing a surface-stabilized, non-agglomerated, silica comprising the steps of: providing colloidal silica in a first solvent; stabilizing the surface of the silica, wherein the stabilizing comprises: performing a solvent exchange operation with an alcohol, whereby the first solvent is exchanged for the alcohol; adding alcohols capable of esterifying the silica; and esterifying the silica to provide stabilized, non-agglomerated silica in alcohol.
The present invention also provides a process for preparing a surface-stabilized, non-agglomerated, silica comprising the steps of: providing colloidal silica in a first solvent; stabilizing the surface of the silica, wherein the stabilizing comprises: performing a solvent exchange operation with a non-aqueous, non-alcohol solvent, whereby the first solvent is exchanged for the non-aqueous, non-alcohol solvent; adding at least one hydrophobating agent to produce provide stabilized, non-agglomerated silica in a non-aqueous, non-alcohol solvent.
The present invention also provides for pneumatic tires, orally inserted compounds, polishing compositions, and inks and toners that use surface-stabilized, non-agglomerated silica of the present invention.
A feature of the invention is the stabilization of silica particles and/or aggregates before they have a chance to agglomerate.
An advantage of the invention is the avoidance of several commercial processing steps to create precipitated silica and then break it down into a size suitable for elastomeric polymer processing.
Another advantage of the invention is cost savings associated with reduction in processing steps. Another advantage of the invention is less variance in size for elastomeric polymer processing, such as physical mixing.
As used throughout this Specification, the following definitions apply:
The term xe2x80x9cslurryxe2x80x9d refers to a thin paste produced by mixing an insoluble substance with enough solvent to allow the mixture to flow viscously.
The term xe2x80x9corganosolxe2x80x9d refers to the colloidal dispersion of an insoluble material in an organic liquid.
The term xe2x80x9calcosolxe2x80x9d refers to the colloidal dispersion of an insoluble material in an alcohol.
The term xe2x80x9cstabilizedxe2x80x9d refers to being substantially unable to form an aggregate or an agglomerate via normal physical means.
The phrase xe2x80x9csolvent exchangexe2x80x9d refers to the process where one solvent replaces another solvent in a solution, slurry, or sol.
The phrase xe2x80x9csurface stabilized, non-agglomerated silicaxe2x80x9d refers to silica that has been surface treated without agglomeration of the silica.
The term xe2x80x9cmasterbatchxe2x80x9d refers to any blend of silica with other additives, such as a blend of modified silica with a polymer; a blend of modified silica, polymer and an oil; and a blend of modified silica, polymer, oil, and other additives.